1. Field of Invention
This invention is directed to a soil, in particular, an artificial soil that is lightweight.
2. Background
In urban environments, roof space provides a triple threat. First, its exposure to the environment and its temperature extremes and moisture conditions provide a high maintenance cost for building owners. Secondly, rooftops produce volumes of urban storm water contributing to non-point pollution and combined sewer overflow. Lastly, the typically black tar surfaces of rooftops contribute to the urban heat island effect and increase the need for power usage and increased use of air conditioning.
To solve this problem, it has been proposed that rooftop urban spaces be used as ecological preserves, by placing soil on the roofs and planting trees, grasses, and other vegetation on the roofs. The use of soil and flora catches and filters water during storms, acts as a leveling thermal barrier between the roof and the ambient atmosphere to cool and filter the atmosphere, increase biodiversity and bird habitat within the city and on large roofs anywhere, while further protecting the roof membrane from damage from ultra violet rays and temperature extremes, including the freeze-thaw cycle, decreasing wear and tear.
However, soil is a complex ecosystem having many characteristics that must be mimicked. Soil serves several functions and has many characteristics, which make it appropriate for supporting plant life. A major fraction of soil is hydrophilic and demonstrates a certain water holding capacity, as well as a capillary action to hold and retain the necessary water, preventing runoff and promoting plant and microbial growth. Furthermore, soil acts as an air and water filter. A root and soil system should also promote microbial film and soil crumb production. Furthermore, soil provides nutrients, such as minerals to plants.
Furthermore, in traditionally urban environments, there is a demand for systems to filter the air, moderate the temperature fluctuations of the environment, and retain and filter water in the environment. One way of doing this, as discussed above, is through the use of herbaceous plants, shrubs and trees in the environment. The flora, in combination with the soil, provides a heat sink and radiator dependent upon water availability and its temperature relative to the environment, capturing storm water, providing shade, and through photosynthesis taking carbon dioxide out of the air and producing oxygen. At the same time, the soil itself not only supports the flora and its function but retains water in its own right and, if sufficiently porous, with high surface area, filters water, prevents unnecessary waste of water through runoff, and filters the air in its own right.
However, much of the available space in urban areas is provided on rooftops or in gardens in the interior of buildings. The use of natural soil on the roof suffers from the disadvantage that it is a dense material, which becomes more dense when saturated with water. Most existing rooftops are not designed to bear loads of over 30 pounds per square foot, a load well below the saturated soil threshold, not including any additional flora planted therein.
Hydroponic gardens, which do away with soil, have been developed to promote flora use in urban settings. However, they suffer from the disadvantage that they do not prevent runoff, do not adequately support a sufficient biomass of flora, and do not perform the other functions of soil, namely filtration of water and air.
Artificial soils are known in the art as known from the lightweight soil developed by the Applicant in 2002. Applicant mixed shredded expanded polystyrene with composted organics. However, the proposed lightweight soil was not hydrophilic, nor did it provide many of the other necessary characteristics of pore size, or structural integrity, to truly mimic the functionality of soil.
Accordingly, lightweight soil capable of mimicking the attributes of a true soil including the hydrophilic and filtering characteristics of the soil is desired.